In the process sequence of manufacturing semiconductor devices, various gas processes, such as a film formation process and an etching process, are repeatedly performed on a target object, such as a semiconductor wafer (which will be simply referred to as “wafer”). A gas process of this kind comprises steps of placing a wafer inside a chamber, and supplying a process gas containing a reactive gas (corrosive gas), such as a halogen, e.g., Cl or F, into the chamber, while vacuum-exhausting the chamber. For example, in a CVD process for forming a Ti-containing film, such as a Ti or TiN film, a wafer is heated to, e.g., about 700° C., and TiCl4 gas serving as a process gas (film formation gas) and a reducing gas are supplied into a chamber set at a predetermined vacuum pressure, so that the film formation process is performed, wherein the process gas is turned into plasma, as needed.
On the other hand, the material of a showerhead disposed inside a chamber is conventionally an Al alloy (such as JIS A 5052) or stainless steel. In a gas process using a halogen-containing gas, such as TiCl4 gas, a component of the showerhead, such as Al, Fe, or Cu, reacts with a hydrogen halide, such as HCl or HF, which is a by-product of the gas process, and a metal halide of this component is thereby generated. The metal halide has a high vapor pressure inside the chamber set at a vacuum pressure and thus can be easily vaporized. Consequently, the metal halide is diffused inside the chamber and generates particles inside the chamber and/or it is taken into a deposited substance during film formation and causes metal contamination on the wafer.
The metal contamination is mixed into Si diffusion layers formed at the bottom of contact holes on the wafer and is easily diffused in Si. Consequently, some of the characteristics of transistors, such as the breakdown voltage and/or ohmic properties, may be deteriorated.
In recent years, patterns formed on wafers have been increasing miniaturized and brought about smaller contact holes with a diameter of about 0.13 μm and smaller Si diffusion layers with a thickness of about 80 nm. Use of Si diffusion layers having a junction at a smaller depth (a shallower junction) makes it prominent for transistors to suffer deterioration in characteristics due to the metal contamination described above. Consequently, there are increasing demands for suppression of such metal contamination. Particularly, where a metal film is formed by CVD, suppression of such metal contamination is very important.
As a technique for solving this problem, Jpn. Pat. Appln. KOKAI Publication No. 2003-313666 discloses a technique for forming an Ni coating film or the like on the surface of members, such as a showerhead, inside a chamber. When Ni comes into contact with a halogen-containing gas, it generates a halide. Since Ni halide has a low vapor pressure and thus cannot be easily vaporized, particle generation inside the chamber is decreased, and metal contamination on wafers is thereby suppressed.
However, where the surface of the showerhead is covered with Ni, a black reaction product may be formed on the showerhead surface due to some reaction and easily peeled off to generate particles after a Ti film or the like is formed. Further, separable parts of the showerhead may be strongly fixed to each other by diffusion bonding of this reaction product. Once compounds of this kind are formed, they can be hardly removed under conditions conventionally used for dry cleaning.